The invention concerns a process for manufacturing soldering rods which contain at least 60 weight-% copper, preferably at least 80 weight-%, and at least one alloy component of the group phosphorus and silver by forming a block of a corresponding copper alloy into a wire at temperatures below the eutectic point.
Copper alloys of the above composition play a very special role as hard solders in soldering technology. Copper-phosphorus and copper-silver-phosphorus alloys are particularly preferred because of their low melting points and their low viscosity. According to DIN 8513 conventional copper alloys include LCU-P6 (6% phosphorus, rest copper) and LCU-P8 (8% phosphorus, rest copper). Also used are copper-silver alloys with a silver percentage between 2 and 15 wt. % (rest copper, optionally containing traces of tin, zinc and lead).
Both the phosphorus-containing and the silver-containing soldering alloys cause significant problems during the manufacture of the soldering rods which are obtained by cutting the wires into segments. Whereas the phosphorus-containing soldering material becomes more and more brittle with an increasing phosphorus content, the silver-containing soldering material is relatively ductile but is slow in gaining fluidity so that the forming speed is limited. Both the brittleness and the slow forming speed obstruct an economical manufacture of soldering rods which have to be produced from a block of a correspondingly large cross section into wires of a smaller cross section by means of extrusion. The diameter and/or cross section of these wires must then subsequently be reduced again by rolling and/or drawing.
Present manufacturing processes make use of completely alloyed cylindrical blocks, also referred to as "slugs", which have a length of 300 mm, a diameter of 83 mm and a weight of approximately 11.8 kg. These blocks are heated up to temperatures between 550 and 600.degree. C. and, by means of extrusion, they are simultaneously formed into several individual wires of desired final dimensions. Between 10 and 20 individual wires are simultaneously produced depending on the cross section of the wire. The handling of the wire bundles, however, which have to be withdrawn from the extruder, is difficult and renders a large-scale industrial production almost impossible. Already the extrusion involves a material loss of more than 5%.
There is further loss of material during the continued manufacture. The bundles of wires that are withdrawn are bonded together more or less strongly due to material adhesion. They are usually cut to conventional lengths of 385 or 500 mm, for example, by shearing or stamping. The quality of these individual rods which are obtained by cutting through an entire bundle of wires is by far not satisfactory with respect to the quality of the cut. Consequently, the cutting results in further loss of material which amounts to approximately 10% of the initially used material.
The rods that were cut to length and provided with dark oxide films must subsequently be pickled in diluted sulfuric acid, then rinsed with water and after the rinsing barrel-polished with wood chips to regain a metallic shine. This process also involves an extraordinary amount of labor and cost since it requires complicated processes for the disposal of sulfuric acid and sulfate solutions to meet requirements of environmental protection.
Although the above described loss of material is only temporary since the alloy can be recovered again by melting, this "recycling" still constitutes a major cost factor that can not be transferred to the customer. Ultimately, the remelting, due to the energy consumption involved, is also an environmental load to be avoided.
Another method that has been applied is the use of extrusion processes to produce wires of larger diameters where the cross section is then reduced by means of rolling and/or drawing thus obtaining, for example, prismatic cross sections such as square cross sections. However, these measures involve an extraordinary amount of labor and cost. In case of phosphorus copper solder this is due to the high brittleness and with respect to the silver-copper solder, it is due to the slow flow speed.
Pages 655 et. seq. of the book by Dr. Ing. Kurt Dies "Kupfer und Kupferlegierungen in der Technik" [Copper and Copper Alloys in Technology], Springer Publishing, 1967, state that the copperphosphorus system can be formed by hot rolling, hot pressing or forging, however only as long as the shaping is carried out in the pure .alpha.-range. According to the phase diagram of page 656, however, the .alpha.-phase already ends at a phosphorus percentage of approximately 2 weight percent.
The eutectic point of the copper-phosphorus system is at 714.degree. C., and the author further states that alloys of a high phosphorus content must be processed at approximately 200.degree. C. below the eutectic point. For a phosphorus content of 8%, a favorable extrusion temperature would hence range between 500.degree. and 530.degree.C. The process, however, faces here a significant form change resistance.
The extrusion process discussed in the introduction is, however, by no means the final step in the manufacture of soldering rods. Page 659 of the same book states that alloys of the copper-phosphorus system with a phosphorus content over 3% can no longer be cold formed by conventional drawing.
The author Dr. Dies further states on page 660 that a pressed eutectic copper-phosphorus alloy with 8.5% phosphorus, for example, can be readily formed at a temperature above 200.degree. C. so that alloys can be hot rolled into thin bands for soldering foils at 300.degree. to 400.degree. C.
This data alone, however, does not allow the economical manufacture of soldering foils nor of soldering wires. It is extremely difficult, for example, to heat up the initial material for soldering foils in a furnace to corresponding temperatures and to subsequently roll it within the temperatures indicated since there is an intimate thermal contact of the thermally well conductive soldering material to its surroundings and to the rolls of the rolling mill which cannot be heated up to corresponding temperatures.
U.S. Pat. No. 1,954,168 discloses soldering material with a phosphorus content between 6 and 9%. Knowing that soldering materials of this kind are difficult to form when the phosphorus content is at 6% and more, the inventor proposed to mix copper with a copper alloy which contains approximately 15% phosphorus. The total phosphorus content, however, should be above 2.5% and below 6%. The corresponding alloy is cast into plates and in numerous passes with a corresponding intermediate heating to temperatures between 350.degree. and 600.degree. C., it is rolled into sheets of approximately 0.5 mm in thickness. The cutting of the thin sheets produces structures similar to those of silver tinsels. The manufacture of soldering rods from practically endless soldering wire is not disclosed. An essentially continuous method of operation is not described either.
Moreover, the known process for manufacturing soldering foils is extremely energy-consuming due to the unfavorable ratio of surface to volume. Especially the relatively high roll temperatures are already in a range where pronounced surface oxidation occurs.
From the publication "Chemical Abstracts, " 1981, volume 94, page , 269, quotation 94:212902 m, it is known to roll ingots of a copper-silver base alloy for soldering purposes with 15% silver and 5% phosphorus at 500 .degree. C. into bands of 3 mm in thickness. Due to oxidation, this process also has the disadvantage that the intermediate products must be pickled in sulfuric acid although the rolling temperatures are significantly below 540.degree. C. This process does not allow the manufacture of soldering rods from a practically endless soldering wire either.